Organic boron compounds are frequently used for organic synthesis due to its easy handling, and at present, more than 300 kinds of organic boron compounds are distributing in the market. In addition, various novel organic boron compounds are being developed.
However, it is difficult to obtain the pure boronic acids because they undergo easily dehydration and trimerization due to forming cyclic anhydride. Therefore, there are any problems that stoichiometric ratio of reactants when used for the reaction is not be determined, and a large amount of boronic acid must be used compared with theoretical amounts, and reagent cost becomes a problem in the case of the expensive reagent. In addition, the well known boronic acids are generally less reactive, therefore, there is a problem of the necessity of activating them by base etc.
Then, in recent years, organic boronic acid esters and organic trifluoroborate potassium salts, which do not undergo trimerization with dehydration, have been developed (Patent Document 3, Non-Patent Document 2). However, these organic boron compounds, also, are less reactive, thus, have such a problem as the necessity of activation treatment, for example, by adding a base etc. in reaction.
In addition, trihydroxy borate salt or trialkoxy borate salt has been investigated (Patent Document 4, Non-Patent Document 1). However, since these have the structure that three hydroxyl groups or alkoxy groups locate independently, these compounds are easily dissociated and less stable, therefore isolation thereof becomes difficult.
Although the other various novel organic boron compounds are being investigated, these compounds are not investigated whether they are able to use as the organic boron reagents or not. (Patent Document 1, Patent Document 2, Patent Document 5).
Moreover, the organic triol borate salts having different structure are disclosed (Non-Patent Document 4).
Further, generally, in the case of cross coupling reaction of organic boronic acid to be carried out in basic aqueous solution, hydrolysis of C—B bonding may be carried out competitively, therefore, a large excess of boronic acid may be required. Such a circumstance is remarkable in hetero aromatic boronic acid, in particular, 2-pyridine boronic acid hydrolyzes very quickly, therefore, due to poor practicality, there are no examples used in reaction.
Under such a circumstance, developments of novel organic boron compounds undergoing no trimerization with dehydration, having high reactivity and excellent storage stability are expected.    [Patent Document 1] JP-A-11-116580    [Patent Document 2] JP-A-2000-212195    [Patent Document 3] CA-A1-2285578    [Patent Document 4] WO 2005/105817    [Patent Document 5] U.S. Pat. No. 2,909,560    [Non patent Document 1] Organic Letters 2006, 8, 4071    [Non patent Document 2] Organic Letters 2006, 8, 761    [Non patent Document 3] Organic Mass spectrometry 1992, 27, 876    [Non patent Document 4] J. Org. Chem., Vol 0.61, No. 17, 1996